Japanese police have arrested the CEO of the failed company MtGox, which was once the world's biggest exchange of the virtual currency, bitcoin.

Mark Karpeles, 30, is being held in connection with the loss of bitcoins worth $387m (£247m, €351m) last February.

He is suspected of having accessed the exchange's computer system to falsify data on its outstanding balance.

MtGox claimed it was caused by a bug but it later filed for bankruptcy. Download Flash Player now You need to install Flash Player to play this content. Media caption The BBC's Rory Cellan Jones explains how Bitcoin works